Oct 27, 2013

Types of Protective Relays and its Function



protective-relays

There are very different functions of protection relays, every one of those relays are ready to touch upon sure type of faults. Every equipment wants different types of protection relays. As example, Distance relays are suitable for transmission lines, and differential relays for power transformers and bus bars. Before undergo protection relays, will see the list different types of protection relays by it’s operate and ANSI code as shown in table below:
      
ANSI Code and Relay Function
ANSI Number
DESCRIPTION
2
Time-delay
21
Distance
25
Synchronism-check
27
Under voltage
30
Annunciator
32
Directional power
37
Undercurrent or under power
38
Bearing
40
Field
46
Reverse-phase
47
Phase-sequence voltage
49
Thermal
50
Instantaneous over current
51
AC time over current
59
Over voltage
60
Voltage balance
63
Pressure
64
Apparatus ground
67
AC directional over current
68
Blocking
69
Permissive
74
Alarm
76
DC over current
78
Out-of-step
79
AC re-closing
81
Frequency
85
Carrier or pilot-wire
86
Lock out
87
Differential
94
Tripping
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